1. Field of the Invention
This invention relates to multi-pole miniature circuit breakers with ground fault protection having a molded housing with separate compartments for each mechanical pole and the ground fault circuits, and more particularly, to such circuit breakers which are able to withstand the higher gas pressures generated by the interruption of higher short circuit currents than conventionally handled by such circuit breakers.
2. Background of Information
Circuit breakers used in residential and light commercial installations are referred to as miniature circuit breakers. Such circuit breakers have molded insulative housings of standard dimensions sized to interchangeably plug into or bolt onto the hot stabs in a load center or panel board. Two-pole miniature circuit breakers incorporate two trip devices in a common housing which occupies two adjacent positions in the load center or panel board.
Examples of a two-pole miniature circuit breaker are provided in U.S. Pat. Nos. 3,999,103 ('103 patent) and 5,260,676 ('676 patent). As is typical for miniature circuit breakers, the two-pole breakers of these patents utilize thermal-magnetic trip devices to provide overload and short circuit trip functions for the protected circuits. These circuit breakers also include an electronic circuit which provides ground fault protection.
The housings for the two-pole ground fault circuit breakers of the '103 and '676 patents essentially comprise two single pole breaker housings bolted together. Each half includes two stacked molded trays forming side-by-side compartments and a cover for the open compartment. The thermal-magnetic trip unit for the pole is mounted in one compartment and part of the circuits for ground fault protection is provided in the other compartment. With the two halves bolted together, the two mechanical poles are separated by one of the electronic compartments. The '676 patent suggests a single, double sized electronic compartment as an alternative, but provides no hint of how that would be implemented.
In the '103 patent most of the ground fault protection circuit is provided in the electronic compartment between the two magnetic poles including a toroidal sensing coil. However, separate trip solenoids are provided for each pole and are located in the respective electronic compartments. These trip solenoids have a lever on the plunger which extends through an opening in the partition between the mechanical pole and the electronic compartment and which engages the thermal-magnetic device to trip the pole.
The '676 patent utilizes a ground fault circuit providing neutral to ground as well as line to ground fault protection. The circuit used requires two toroidal coils which occupy the electronic compartment between the two mechanical pole compartments. The remainder of the electronic circuitry, including a single trip solenoid with separate windings for the two poles, is located in the other electronic compartment.
This splitting of the electronic trip circuit as described in both the '103 and '676 patents necessitates the routing of wires between the two electronic compartments in addition to the routing of wires from the mechanical poles to the electronic compartments. This complicates the task of assembling the two pole ground fault circuit breaker. In addition, the widths of the two electronic compartments are limited. This limited width dictated that the toroidal coils in the '676 patent, and the output transformer in the '103 patent used in the ground fault circuit had to be mounted with their central axes crosswise within the main electronic compartment.
There is an interest in increasing the current rating of the two pole circuit breaker. While each mechanical pole of the current two pole miniature circuit breakers has a gas vent which provides an escape for the gases generated by arcing during interruption of a short circuit, when the current rating of these breakers was increased from 15 amps to above 50 amps, the housing could not withstand the gas pressures generated.
Duplex miniature circuit breakers have been made available which combine two circuits in side-by-side compartments drawing power from the same phase through a common line terminal. An opening in the partition between the compartments allows gases generated by interruption of current in one circuit to expand into both compartments. These duplex miniature circuit breakers do not have electronic trip circuits.
There is a need therefore, for an improved two-pole ground fault circuit breaker.
More particularly, there is a need for such a circuit breaker with a higher current rating than is currently provided.
There is yet another need for such a circuit breaker which has a housing with fewer parts and is easier to assemble.